My 2021 Silverado 1500 has had a "Service Rear Axle" message come up on the dash about a year ago, I have been back to the dealer a number of times and they are unable fix or delete and don't have a solution for me, further to that the message is not listed in the manual and does not show up as a fault when the car is checked with a scan tool........ I don't even believe that the diff has a sensor in it in the first place, has anyone heard of or seen this message before?
I have also lost the picture of the car on the tyre pressure page/ image below.

 

You have electrical issues. Have your system load tested.

 

Thanks for your help, but sorry I took the image as I turned the car on and the voltage was still going up, it sits just under 14v when the car is running.